A famous ad campaign in the late 1970s featured members of the International Ladies’ Garment Workers’ Union singing “Look for the Union Label.” Now, more than thirty years later, that label is getting harder to find on manufactured products.

The Wall Street Journal recently reported that a smaller percentage of the private sector workforce is composed of union members:

Organized labor lost 10% of its members in the private sector last year, the largest decline in more than 25 years. The drop is on par with the fall in total employment but threatens to significantly limit labor’s ability to influence elections and legislation.

On Friday, the Labor Department reported private-sector unions lost 834,000 members, bringing membership down to 7.2% of the private-sector work force, from 7.6% the year before. The broader drop in U.S. employment and a small gain by public-sector unions helped keep the total share of union membership flat at 12.3% in 2009. In the early 1980s, unions represented 20% of workers.

Labor experts said the union-membership losses would have a long-term impact on unions and their finances, because unions wouldn’t automatically regain members once the job market rebounded. In many cases, new jobs will be created at nonunion employers or plants.

The recession has been particularly hard on the manufacturing sector and construction industries, both of which tend to be heavily unionized. But there is one sector of the job market where labor unions are seeing steady growth in the numbers of their members who are among the employed:

For the first time in American history, a majority of union members are government workers rather than private-sector employees, the Bureau of Labor Statistics announced on Friday.

In its annual report on union membership, the bureau undercut the longstanding notion that union members are overwhelmingly blue-collar factory workers. It found that membership fell so fast in the private sector in 2009 that the 7.9 million unionized public-sector workers easily outnumbered those in the private sector, where labor’s ranks shrank to 7.4 million, from 8.2 million in 2008.

Indeed, among government workers, union membership rose to 37.4 percent last year, a 0.6 percent increase over 2008. Looking only at government employment figures, one would be hard pressed to know that the nation is in a recession, as government employment grew by 16,000 jobs to 22,516,000, according to the labor bureau.

Fred Siegel, a senior fellow at the Manhattan Institute, says that we may see some political fallout over the situation in which public-sector workers are now the majority in organized labor:

“At the same time the country is being squeezed, public-sector unions are a rising political force in the Democratic Party,” he said. “They depend on extra money for the public sector, and that puts the Democrats in a difficult position. In four big states — New York, New Jersey, Illinois and California — the public-sector unions have largely been untouched by the economic downturn. In those states, you have an impeding clash between the public-sector unions and the public at large.”

With jobs at or near the top of voter concerns in this mid term election year, the growth in public sector employment, regardless of whether those workers have union affiliation, could well become a major campaign issue in 2010.